Read my post again. It is not about the IP you use to create the accounts. It is about the IP you use to bot.
Example based on a real experiment. I bought 10 tutorial island accounts from a guy which were made under the same IP address '1.0.0.0' and I log in to those 10 accounts to check whether they work or not under my IP '2.0.0.0'. I then log out and just bot in one of them. If it gets caught, all of my accounts will be banned if my IP is flagged. That really happened to me and I lost all of them when I only botted in one. Now his IP is not flagged, it is mine. RuneScape checks for the last IP you used to log in or the one when caught while botting.
Only if my IP was not flagged, I was only going to lose that account and not all of them.